The present application relates to construction equipment, such as cranes. In particular, the present application relates to a crane having arms for raising a mast, i.e., a self-raising mast. The present application also relates to a method of self-raising the mast and assembling the crane.
Construction equipment, such as cranes or excavators, must often be moved from one job site to another. Moving a crane or an excavator can be a formidable task when the machine is large and heavy. For example, highway limits on vehicle-axle loads must be observed, and overhead obstacles can dictate long, inconvenient routings to the job site.
One solution to improving the mobility of large construction machines, such as cranes, is to disassemble them into smaller, more easily handled components. The separate components can then be transported to the new job site where they are reassembled.
The typical practice has been to use an assist crane to disassemble the crane into the separate components. The assist crane is then used to load the components onto their respective transport trailers. Once at the new job site, another assist crane is used to unload the components and reassemble the crane.
As the components for a large crane can weigh in excess of 80,000 lbs., the capacity of the assist crane required represents a very significant transport expense. As a result, designers have attempted to develop self-handling systems for assembling and disassembling cranes. The majority of the self-handling systems developed thus far have been directed to smaller cranes that only need to be disassembled into a few components.
The development of self-handling systems for larger cranes, however, has met with limited success. One reason for this is that larger cranes need to be disassembled into numerous components, thus requiring time-consuming disassembly and reassembly procedures. For example, a large capacity crane typically uses a complicated and cumbersome rigging system to control the angle of the boom. Boom rigging system components such as the equalizer, the mast, and wire rope rigging are heavy and difficult to disassemble for transport.
Another reason for the limited success of prior art self-assembling cranes is that they typically rely on additional crane components that are used only for assembling and disassembling the crane. For example, some self-assembling cranes require additional wire rope guides and sheaves on the boom butt so that a load hoist line can be used with the boom butt to lift various crane components during the assembly process.
An example of a prior art method for assembling and disassembling a typical large capacity crawler crane is disclosed in U.S. Pat. No. 5,484,069, titled “Process For Self-Disassembling A Crawler Crane” (“the '069 patent”). In particular, this patent is directed to a type of crawler crane having a mast that is supported by a backhitch.
Another example of a prior art method for assembling and is assembling a different type of crawler crane is disclosed in U.S. Pat. No. 6,062,405, titled “Hydraulic Boom Hoist Cylinder Crane” (“the'405 patent”). This patent is directed to a type of crane that utilizes hydraulic cylinders to control the angle of the boom.
The '069 patent and the'405 patent are both examples of self-assembling cranes that require the use of the boom butt to lift and position components for assembly on to the crane. As a consequence, additional sheaves must be included on the boom butt for the self-assembling procedure. It is therefore desirable to provide a crane and method of self-assembly which eliminates, or at least reduces, the use of the boom butt during the self-assembling procedure.
In addition to the above, some types of cranes utilize a moving or live mast. A crane having a moving or live mast is connected directly to the boom by one or more boom pendants. The boom angle is controlled by boom hoist rigging, which is connected between the mast and the upper works of the crane. The mast and the boom move together as the boom angle is changed. The mast must typically be disconnected from the boom and stored horizontally on top of the crane for transport between job sites. Moreover, the masts on these types of cranes are often very long and heavy, and are consequently difficult to handle during the assembly process. It is therefore desirable to provide a crane having a self-raising mast. It is also desirable to provide a system and method of controlling the mast self-raising procedure that is safe, efficient and easy to implement.
Another of the challenges to having a self-raising mast is the limited space on a crane's upper works or rotating bed in which to install the raising mechanism. For example, it is desirable to install a linear actuator, such as a hydraulic cylinder with an extension rod, that provides as nearly perpendicular force to the mast throughout its course of travel as possible. Of course, since the mast typically rotates about a fixed point on the rotating bed, the force of the cylinder rarely is perpendicular. That said, when the mast is positioned in a near horizontal position it is most efficient for the hydraulic cylinder to be positioned near vertically so that the extension rod presses most closely to a perpendicular position relative to the mast. The problem, however, with such an arrangement is that the hydraulic cylinder extends through a portion or all of the rotating bed. There simply may not be sufficient space to position the hydraulic cylinder vertically, then.
Alternatively, the linear actuator, such as a hydraulic cylinder or other raising mechanism, could be positioned at an angle to the mast rather than nearly vertically. Thus, the closer to parallel the linear actuator lies to the mast, the less vertical space within the rotating bed that the linear actuator occupies. The drawback to this solution, however, is that the closer to parallel that the actuator lies relative to the mast, the force normal to the mast that the actuator applies decreases. In other words, it is relatively more difficult for an actuator, such as a hydraulic cylinder, of a given size to raise a mast when it is positioned more closely to parallel with the mast.
To overcome this, and to apply a greater force normal to the mast, one can increase the size and/or capacity of the cylinder. This would result in more force being applied normal to the mast, but much of the additional capacity of the larger hydraulic cylinder is wasted because it is applied in a direction parallel to the mast. Further, the benefits of packaging the cylinder at an angle to the mast in terms of providing greater available space in the rotating bed are defeated, in part, by increasing the size/capacity of the hydraulic cylinder. In other words, solving the problem of space in the vertical direction of the rotating bed may simply create a problem of insufficient space in an angled and/or horizontal direction of the rotating bed.
In U.S. Pat. No. 6,695,158, titled “Crane With Self-Raising Mast” (the “'158 patent”), a crane has an upper works rotatably mounted on a lower works, a boom pivotally mounted on the upper works, a mast pivotally mounted on the upper works and pendantly connected to the boom, and boom hoist rigging connected to the mast for controlling the angle of the boom. The invention further comprises a self-raising mast assembly for controlling the position of the mast when the mast is not connected to the boom. The self-raising mast assembly comprises a mast raising yoke, a hydraulic mast raise cylinder, and a hydraulic system.
The '158 solves some of the issues discussed with the prior art, but it involves several components that rotate and are pinned together, increasing the complexity of the mechanism. Further, it involves positing the hydraulic cylinder in relatively vertical position within the rotating bed of the crane, which consumes a significant amount of vertical space in the rotating bed.
It is therefore desirable to provide a crane and method of self-assembly which is mechanically simple relative to the prior art and reduces the amount of space into which it is packaged or positioned within the rotating bed.